Variable Displacement Vane Pump

ABSTRACT

A variable displacement vane pump has an inner peripheral face of a cam ring formed so that in a maximum eccentric state, a radius vector gradually shortens according to the rotation of a rotor in an area from a starting point of a first seal interval to an intermediate point of the first seal interval and an area from an intermediate point of a second seal interval to an end point of the second seal interval. The inner peripheral face of the cam ring is formed so that in a minimum eccentric state, the radius vector is substantially fixed or gradually lengthens according to the rotation of the rotor in other areas.

BACKGROUND

1. Technical Field

The present invention relates to a variable displacement vane pump used for working fluid application equipment such as a power steering for reducing a steering wheel operating force of an automobile for example.

2. Related Art

For the well-known technology related to this type of variable displacement vane pump, a variable displacement pump (JP-A No. 2002-115673) can be given for an example, the variable displacement pump having structure that an inside diameter in an intermediate interval between a suction interval and a discharge interval in a pump room of a cam ring forms a negative sloping curve with an end of a suction port as a starting point so as to prevent a pulsation phenomenon of working fluid in a large eccentric area of the cam ring and further, the negative sloping curve and a complete round curve are connected by a higher order curve.

Generally, in a variable displacement vane pump, in a fixed displacement area equivalent to a low-speed area of the pump in which discharge per one rotation is fixed, when a situation in which a vane is separated from an inner peripheral face of a cam ring occurs, pressure pulsation is caused or in a variable displacement area equivalent to a high-speed area of the pump in which discharge per one rotation decreases as the rotation speed of the pump increases, vibration is apt to grow by the unbalance of pressure, compared with a case of a fixed displacement vane pump, and as noise is made by the pressure pulsation and the vibration, it has been a technical objective to reduce such noise.

In the variable displacement vane pump disclosed in JP-A No. 2002-115673, to reduce noise by the separation of a vane, in a maximum eccentric state in which the eccentricity to a rotor of the cam ring is maximum, a distance to the rotational center of the rotor is made to gradually shorten according to the rotation of the rotor in an area from a termination of a suction port to a starting end of a discharge port and an area from a termination of the discharge port to a starting end of the suction port on an inner peripheral face of the cam ring, hereby, the separation of the vane is prevented and the occurrence of noise is restrained.

However, as the compressibility of the volume of the pump room increases in a variable displacement area and peak pressure grows when the inner peripheral face of the cam ring has such a shape, the variable displacement vane pump has a problem that noise by vibration is apt to be made.

In short, the variable displacement vane pump disclosed in JP-A No. 2002-115673 has structure that even if the separation of the vane in a fixed displacement area is restrained and the occurrence of noise caused by pressure pulsation can be prevented, a peak of pressure in the pump room in the variable displacement area is not restrained and it is difficult to prevent the occurrence of noise by vibration.

SUMMARY

The present invention is made in view of such a problem and a technical object of the present invention is to provide a variable displacement vane pump having structure that the separation of a vane in a fixed displacement area and a peak of pressure in a pump room in a variable displacement area are restrained and the occurrence of noise caused by pressure pulsation and vibration can be fully prevented.

To achieve the technical object, in accordance with a first feature of the present invention, there is provided a variable displacement vane pump for transmitting steering operation on a steering wheel to a steered wheel and supplying working fluid to a steering gear for a vehicle that generates steering assist force by hydraulic pressure of the working fluid. The variable displacement vane pump includes a pump housing equipped with a pump element storage part, a driving shaft journaled to the pump housing, a rotor provided in the pump housing, rotatively driven by the driving shaft and having plural slots in a circumferential direction, plural vanes provided in a freely projecting/retreating manner in the plural slots, a cam ring annularly formed movably on/over the pump element storage part and forming plural pump rooms together with the rotor and the plural vanes on an inner peripheral side and a cam ring control mechanism that is provided to the pump housing and controls eccentricity to the rotor of the cam ring. The pump housing is provided with a suction port open to an area in which volume of the plural pump rooms increases according to the rotation of the rotor and a discharge port open to an area in which the volume of the plural pump rooms decreases. An inner peripheral face of the cam ring is formed so that in a maximum eccentric state in which eccentricity to the rotor of the cam ring is maximum, a distance to the rotational center of the rotor gradually shortens according to the rotation of the rotor in at least one of an area from a termination of the suction port to an intermediate point of the termination of the suction port and a starting end of the discharge port and an area from an intermediate point of a termination of the discharge port and a starting end of the suction port to the starting end of the suction port in a rotational direction of the rotor, and the inner peripheral face of the cam ring is formed so that in a minimum eccentric state in which the eccentricity to the rotor of the cam ring is minimum, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of an area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and at least a part of an area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port.

In accordance with a second feature, in addition to the first feature, the driving shaft is rotatively driven by an engine of the vehicle and the inner peripheral face of the cam ring is formed so that when the vehicle is run, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port.

In accordance with a third feature, in addition to the first feature, the driving shaft is rotatively driven by the engine of the vehicle and the inner peripheral face of the cam ring is formed so that when engine speed is 1500 rpm or more every minute, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port.

In accordance with a fourth feature, in addition to the first feature, the inner peripheral face of the cam ring is formed so that in the maximum eccentric state, at least one of the area from the termination of the suction port to the intermediate point of the termination of the suction port and the starting end of the discharge port and the area from the intermediate point of the termination of the discharge port and the starting end of the suction port to the starting end of the suction port and areas before and after at least the one that connect with at least the one are connected by a higher order curve and the inner peripheral face of the cam ring is formed so that in the minimum eccentric state, at least one of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and the area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port and areas before and after at least the one that connect with at least the one are connected by a higher order curve.

In accordance with a fifth feature, in addition to the first feature, the inner peripheral face of the cam ring is formed so that in the minimum eccentric state, the distance to the rotational center of the rotor gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port.

In accordance with a sixth feature, in addition to the first feature, the eccentricity to the rotor of the cam ring is controlled by swinging or rolling the cam ring in a state in which the cam ring is supported by a supporting face provided on a side of the discharge port of an inner peripheral face of the pump element storage part.

In accordance with a seventh feature, in addition to the sixth feature, the center of an inside diameter of the cam ring is located on the side of the suction port apart from the center of the rotor in an unloaded condition in which differential pressure between pressure on the side of the suction port and pressure on the side of the discharge port does not act on the driving shaft, the rotor and the cam ring, and in a state in which the driving shaft is elastically deformed on the side of the suction port by the action of the differential pressure, a relative position based upon a port reference line is located on the side of the discharge port apart from the relative position in the unloaded condition the cam ring is rollably supported by the supporting face provided on the side of the discharge port of the inner peripheral face of the pump element storage part and the supporting face is formed so that the center of the inside diameter of the cam ring gradually separates on the side of the discharge port from the port reference line as the cam ring is rolled in a direction from the maximum eccentric state to the minimum eccentric state.

In accordance with an eighth feature, in addition to the first feature, the inner peripheral face of the cam ring is formed so that in the maximum eccentric state, the distance to the rotational center of the rotor gradually shortens according to the rotation of the rotor in the area from the termination of the suction port to the intermediate point of the termination of the suction port and the starting end of the discharge port in the rotational direction of the rotor and the inner peripheral face of the cam ring is formed so that in the minimum eccentric state, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least a part of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port.

In accordance with a ninth feature, in addition to the eighth feature, the inner peripheral face of the cam ring is formed so that in the maximum eccentric state, the distance to the rotational center of the rotor gradually shortens according to the rotation of the rotor in the area from the termination of the suction port to the intermediate point of the termination of suction port and the starting end of the discharge port and the area from the intermediate point of the termination of the discharge port and the starting end of the suction port in the rotational direction of the rotor and the inner peripheral face of the cam ring is formed so that in the minimum eccentric state, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least a part of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port.

In accordance with a tenth feature, in addition to the first feature, the plural odd slots and the plural odd vanes are provided to the rotor.

In accordance with an eleventh feature of the present invention, there is provided a variable displacement vane pump for transmitting steering operation on a steering wheel to a steered wheel and supplying working fluid to a steering gear for a vehicle that generates steering assist force by the hydraulic pressure of the working fluid. The variable displacement vane pump includes a pump housing equipped with a pump element storage part, a driving shaft journaled to the pump housing, a rotor provided in the pump housing, rotatively driven by the driving shaft and having plural slots in a circumferential direction, plural vanes provided in a freely projecting/retreating manner in the plural slots, a cam ring annularly formed movably on/over the pump element storage part and forming plural pump rooms together with the rotor and the plural vanes on an inner peripheral side and a cam ring control mechanism that is provided to the pump housing and controls eccentricity to the rotor of the cam ring. The pump housing is provided with a suction port open to an area in which volume of the plural pump rooms increases according to rotation of the rotor and a discharge port open to an area in which the volume of the plural pump rooms decreases, and an inner peripheral face of the cam ring is formed so that in a maximum eccentric state in which the eccentricity to the rotor of the cam ring is maximum, a distance to the rotational center of the rotor gradually shortens according to the rotation of the rotor in at least one of an area from a termination of the suction port to a starting end of the discharge port in a rotational direction of the rotor and an area from a termination of the discharge port to a starting end of the suction port and the inner peripheral face of the cam ring is formed so that in a minimum eccentric state in which the eccentricity to the rotor of the cam ring is minimum, distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.

In accordance with a twelfth feature, in addition to the eleventh feature, the driving shaft is rotatively driven by an engine of the vehicle and the inner peripheral face of the cam ring is formed so that when the vehicle is run, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.

In accordance with a thirteenth feature, in addition to the eleventh feature, the driving shaft is rotatively driven by the engine of the vehicle and the inner peripheral face of the cam ring is formed so that when engine speed is 1500 rpm or more every minute, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.

In accordance with a fourteenth feature, in addition to the eleventh feature, the eccentricity to the rotor is controlled by swinging or rolling the cam ring in a state in which the cam ring is supported by a supporting face provided on a side of the discharge port of an inner peripheral face of the pump element storage part.

In accordance with a fifteenth feature, in addition to the fourteenth feature, the center of an inside diameter of the cam ring is located on the side of the suction port based upon a port reference line that joins the intermediate point of the termination of the suction port and the starting end of the discharge port and the center of the rotor in an unloaded condition in which differential pressure between pressure on the side of the suction port and pressure on the side of the discharge port does not act on the driving shaft, the rotor and the cam ring, a relative position based upon the port reference line in the unloaded condition in a state in which the driving shaft is elastically deformed on the side of the suction port by the action of the differential pressure is located on the side of the discharge port apart from the relative position the cam ring is rollably supported by the supporting face provided on the side of the discharge port of the inner peripheral face of the pump element storage part and the supporting face is formed so that the center of the inside diameter of the cam ring gradually separates from the port reference line as the cam ring is rolled in a direction from the maximum eccentric state to the minimum eccentric state.

In accordance with a sixteenth feature of the present invention, there is provided a variable displacement vane pump for transmitting steering operation on a steering wheel to a steered wheel and supplying working fluid to a steering gear for a vehicle that generates steering assist force by the hydraulic pressure of the working fluid. The variable displacement vane pump includes a pump housing equipped with a pump element storage part, a driving shaft journaled to the pump housing, a rotor provided in the pump housing, rotatively driven by the driving shaft and having plural slots in a circumferential direction, plural vanes movably provided in the plural slots, a cam ring annularly formed movably on/over the pump element storage part and forming plural pump rooms together with the rotor and the plural vanes on an inner peripheral side and a cam ring control mechanism that is provided to the pump housing and controls eccentricity to the rotor of the cam ring. The pump housing is provided with a suction port open to an area in which volume of the plural pump rooms increases according to rotation of the rotor and a discharge port open to an area in which the volume of the plural pump rooms decreases, an inner peripheral face of the cam ring is formed so that in a maximum eccentric state in which the eccentricity to the rotor of the cam ring is maximum in a state in which the cam ring is relatively moved from the side of the suction port to the side of the discharge port by the action on the driving shaft, the rotor and the cam ring of differential pressure between pressure on the side of the suction port and pressure on the side of the discharge port, compared with an unloaded condition in which no differential pressure acts, a distance to the rotational center of the rotor gradually shortens according to the rotation of the rotor in at least one of an area from a termination of the suction port to a starting end of the discharge port in a rotational direction of the rotor and an area from a termination of the discharge port to a starting end of the suction port and the inner peripheral face of the cam ring is formed so that in a minimum eccentric state in which the eccentricity to the rotor of the cam ring is minimum, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.

In accordance with a seventeenth feature, in addition to the sixteenth feature, the driving shaft is rotatively driven by an engine of the vehicle and the inner peripheral face of the cam ring is formed so that when the vehicle is run, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.

In accordance with an eighteenth feature, in addition to the sixteenth feature, the driving shaft is rotatively driven by the engine of the vehicle and the inner peripheral face of the cam ring is formed so that when engine speed is 1500 rpm or more every minute, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.

In accordance with a nineteenth feature, in addition to the sixteenth feature, the eccentricity to the rotor of the cam ring is controlled by swinging or rolling the cam ring in a state in which the cam ring is supported by a supporting face provided on a side of the discharge port of an inner peripheral face of the pump element storage part.

In accordance with a twentieth feature, in addition to the nineteenth feature and has a characteristic that the center of an inside diameter of the cam ring is located on the side of the suction port apart from a port reference line that joins an intermediate point of the termination of the suction port and the starting end of the discharge port and the center of the rotor in the unloaded condition in which differential pressure between pressure on the side of the suction port and pressure on the side of the discharge port does not act on the driving shaft, the rotor and the cam ring, a relative position based upon the port reference line in a state in which the driving shaft is elastically deformed on the side of the suction port by the action of the differential pressure is located on the side of the discharge port apart from the relative position in the unloaded condition, the cam ring is rollably supported by the supporting face provided on the side of the discharge port of the inner peripheral face of the pump element storage part and the supporting face is formed so that the center of the inside diameter of the cam ring gradually separates from the port reference line as the cam ring is rolled in a direction from the maximum eccentric state to the minimum eccentric state.

According to the variable displacement vane pump of the present invention, as the variable displacement vane pump has the structure in which both the separation of the vane in the fixed displacement area and a peak of pressure in the pump room in the variable displacement area can be restrained by devising a shape of the inner peripheral face of the cam ring, noise can be fully prevented from being made by pressure pulsation and vibration independent of whether the variable displacement vane pump is operated in the fixed displacement area or in the variable displacement area.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described in detail based on the following drawings, wherein:

FIG. 1 is a side view showing basic structure of a variable displacement vane pump equivalent to a first embodiment of the present invention as a section viewed along an extended direction of a driving shaft;

FIG. 2 is a sectional view showing a maximum eccentric state in which eccentricity to a rotor of a cam ring in the variable displacement vane pump equivalent to the first embodiment of the present invention is maximum and viewed along line A-A in FIG. 1;

FIG. 3 is a sectional view showing a minimum eccentric state in which the eccentricity to the rotor of the cam ring in the variable displacement vane pump equivalent to the first embodiment of the present invention is minimum and viewed along line A-A in FIG. 1;

FIG. 4 is a schematic drawing showing relative positional relation among an inner peripheral face of the cam ring, a suction port and a discharge port respectively in a pressure plate, in the maximum eccentric state illustrated in FIG. 2;

FIG. 5 is a schematic drawing showing relative positional relation among the inner peripheral face of the cam ring, the suction port and the discharge port respectively in the pressure plate in the minimum eccentric state illustrated in FIG. 3;

FIGS. 6A to 6C are characteristic line drawings showing a distance between the rotational center of the rotor and the inner peripheral face of the cam ring in a first seal interval in the variable displacement vane pump equivalent to the first embodiment of the present invention, FIG. 6A is the characteristic line drawing showing a radius vector to an angle in the maximum eccentric state, FIG. 6B is the characteristic line drawing showing the radius vector to the angle in the minimum eccentric state, and FIG. 6C is the characteristic line drawing showing the volume to a central angle of a vane chamber in the minimum eccentric state;

FIGS. 7A to 7C are characteristic line drawings showing a distance between the rotational center of the rotor and the inner peripheral face of the cam ring in a second seal interval in the variable displacement vane pump equivalent to the first embodiment of the present invention, FIG. 7A is the characteristic line drawing showing a radius vector to an angle in the maximum eccentric state, FIG. 7B is the characteristic line drawing showing the radius vector to the angle in the minimum eccentric state, and FIG. 7C is the characteristic line drawing showing the volume to a central angle of a vane chamber in the minimum eccentric state;

FIG. 8 is a schematic drawing showing a section of a local part to explain the mechanism of the separation of a vane caused in structure before improvement in the variable displacement vane pump equivalent to the first embodiment of the present invention;

FIG. 9 is a characteristic line drawing showing pressure to an angle to explain a peak of pressure in a vane chamber caused in the structure before improvement in the variable displacement vane pump equivalent to the first embodiment of the present invention; and

FIGS. 10A and 10B are schematic drawings showing relative positional relation among a rotor, a cam ring, a discharge port and a suction port in relation to a supporting face provided to an adapter in a variable displacement vane pump equivalent to a fifth embodiment of the present invention, FIG. 10A is the schematic drawing showing the relative positional relation in a maximum eccentric state, and FIG. 10B is the schematic drawing showing the relative positional relation in a minimum eccentric state.

DETAILED DESCRIPTION

Referring to the drawings, some embodiments of a variable displacement vane pump according to the present invention will be described in detail below.

First Embodiment

FIG. 1 is a side view showing basic structure of a variable displacement vane pump 1 equivalent to a first embodiment of the present invention as a section viewed along an extended direction of a shaft 13 which is a driving shaft. FIG. 2 is a sectional view viewed along line A-A in FIG. 1 in a state that the eccentricity to a rotor 11 of a cam ring 15 in the variable displacement vane pump 1 is maximum. FIG. 3 is a sectional view viewed along line A-A in FIG. 1 in a state that the eccentricity to the rotor 11 of the cam ring 15 in the variable displacement vane pump 1 is minimum. FIG. 4 is a schematic drawing showing relative positional relation among an inner peripheral face of the cam ring 15, a suction port 22 and a discharge port 21 respectively in a pressure plate 27, in the maximum eccentric state illustrated in FIG. 2. FIG. 5 is a schematic drawing showing relative positional relation among the inner peripheral face of the cam ring 15, the suction port 22 and the discharge port 21 respectively in the pressure plate 27, in the minimum eccentric state illustrated in FIG. 3. Besides, FIG. 1 corresponds to the section viewed along line B-B in FIG. 2. Dotted lines shown in FIGS. 4 and 5 show cases in which the inner peripheral face of the cam ring 15 forms a complete round.

As shown in these drawings, the variable displacement vane pump 1 has body structure as a pump housing configured by matching a recessed front body 10 in which pump components including the rotor 11, a vane 14, the cam ring 15, an adapter 12, the pressure plate 27 and a control valve 30 are incorporated and inserted and a rear cover 19.

A shaft 13 which is a driving shaft for transmitting driving force from an external device connects with the rotor 11 of these components and the shaft 13 is supported by the front body 10 via a bearing 28. Plural (for example, odd) slots 29 are provided to the rotor 11 and the vane 14 in a radially freely projecting/retreating manner in each slot 29 is inserted into each slot. A vane bottom 31 is provided at an inner end of each slot 29. The rotor 11 is rotatively driven by the shaft 13.

The adapter 12 is fitted into a recess of the front body 10 and the cam ring 15 swingably supported by the inside of the adapter 12 with a supporting pin 16 as the center is arranged in a state that the center of its inside diameter is eccentric to the rotational center of the rotor 11. A first fluid pressure chamber 34 is formed on the left side of the cam ring 15 as shown in FIG. 2 by the cam ring 15 and the adapter 12, and a second fluid pressure chamber 35 is formed on the right side. The cam ring 15 is pressed by a compression coil spring 17 in a direction in which the pumping capacity of a vane chamber 18 is maximum.

Space between the rotor 11 and the cam ring 15 is partitioned by the vane 14 and plural vane chambers 18 are formed. The discharge port 21 as an outlet is connected to an area the volume of which is reduced by counterclockwise rotation in FIG. 2 of each vane chamber 18 and the suction port 22 as an inlet is connected to an area the volume of which is increased. Besides, the pressure plate 27 is fitted between a group of the rotor 11, the cam ring 15, the vane 14 and the adapter 12 and the front body 10.

The control valve 30 is configured by a valve hole 30 a formed in the front body 10, a spool 30 b slidably arranged in the valve hole 30 a and a spring 30 c. A spring chamber 36 is provided on the side of one end of the control valve 30 and the spring 30 c is installed in the spring chamber 36. The control valve 30 is almost operated according to relation among force by pressure in a control valve high pressure chamber 37 on the side of other end, force by pressure in the spring chamber 36 on the side of the one end and force by biasing force of the spring 30 c. When rightward force in FIG. 2 by difference in pressure between the control valve high pressure chamber 37 and the spring chamber 36 is larger than leftward force by the spring 30 c and the spool 30 b is moved rightward, a channel to a passage 33 that connects with the control valve high pressure chamber 37 and the first fluid pressure chamber 34 is widened as a result and a channel between the passage 33 and the side of a tank not shown is narrowed.

Incidentally, the control valve 30, the first fluid pressure chamber 34, the second fluid pressure chamber 35 and others respectively provided to the front body 10 function as a cam ring control mechanism for controlling the eccentricity to the rotor 11 of the cam ring 15 by fluid pressure in operation in collaboration.

A contour of the inner peripheral face of the cam ring 15 will be described below. The cam ring 15 is in the maximum eccentric state that the center of its inside diameter is located in the most eccentric position to the rotational center Or of the rotor 11 as shown in FIG. 4 in such a state as shown in FIG. 2 in which the pump is unoperated. Besides, by operation described later, the cam ring 15 shown in FIG. 3 is turned the minimum eccentric state that the center of its inside diameter is moved in a direction in which the eccentricity to the rotational center Or of the rotor 11 is reduced and the eccentricity is minimum in an operable range as shown in FIG. 5.

A distance between the rotational center Or of the rotor 11 and the inner peripheral face of the cam ring 15 is called a radius vector, in an interval from a termination of the suction port 22 to a starting end of the discharge port 21 in a rotational direction of the rotor 11, the vanes 14 seal the vane chamber 18 for pressure on the tank and the vane chamber 18 for discharge pressure, the interval is called a first seal interval, and the similar interval from a termination of the discharge port 21 to a starting end of the suction port 22 is called a second seal interval.

FIGS. 6A to 6C are characteristic line drawings showing a distance between the rotational center Or of the rotor 11 and the inner peripheral face of the cam ring 15 in the first seal interval in the variable displacement vane pump 1, FIG. 6A is the characteristic line drawing showing the radius vector to an angle in the maximum eccentric state, FIG. 6B is the characteristic line drawing showing the radius vector to the angle in the minimum eccentric state, and FIG. 6C is the characteristic line drawing showing the volume of the vane chamber 18 to its central angle in the minimum eccentric state. FIGS. 7A to 7C are characteristic line drawings showing a distance between the rotational center Or of the rotor 11 and the inner peripheral face of the cam ring 15 in the second seal interval in the variable displacement vane pump 1, FIG. 7A is the characteristic line drawing showing the radius vector to an angle in the maximum eccentric state, FIG. 7B is the characteristic line drawing showing the radius vector to the angle in the minimum eccentric state, and FIG. 7C is the characteristic line drawing showing the volume of the vane chamber 18 to its central angle in the minimum eccentric state. Dotted lines in the characteristic line drawings in FIGS. 6A to 6C and FIGS. 7A to 7C show cases in which the inner peripheral face of the cam ring 15 forms a complete round.

To put it concretely, relation between the angle and the radius vector in the maximum eccentric state shown in FIG. 4 is shown as a characteristic line in the first seal interval in FIG. 6A, and in FIG. 7A, a characteristic line showing relation between the angle and the radius vector in the maximum eccentric state in the second seal interval is similarly shown.

Referring to FIGS. 6A and 7A, the inner peripheral face of the cam ring 15 in the first embodiment is formed so that the radius vector gradually shortens in an area from a starting point of the first seal interval (the termination of the suction port 22) to an intermediate point of the first seal interval (an intermediate point of the termination of the suction port 22 and the starting end of the discharge port 21) and in an area from an intermediate point of the second seal interval (an intermediate point of the termination of the discharge port 21 and the starting end of the suction port 22) to an end point of the second seal interval (the starting end of the suction port 22).

Besides, when the cam ring 15 is moved to be in the minimum eccentric state shown in FIG. 5, relation between the angle and the radius vector varies as shown in the characteristic line drawings in the minimum eccentric state in FIGS. 6B and 7B. Then, referring to FIGS. 6B and 7B, the inner peripheral face of the cam ring 15 in the first embodiment is formed so that the radius vector is substantially fixed or gradually lengthens according to the rotation of the rotor 11 in at least a part of an area from the intermediate point of the first seal interval (the intermediate point of the termination of the suction port 22 and the starting end of the discharge port 21) to the end point of the first seal interval (the starting end of the discharge port 21) and in at least a part of an area from a starting point of the second seal interval (the termination of the discharge port 21) to the intermediate point of the second seal interval (the intermediate point of the termination of the discharge port 21 and the starting end of the suction port 22).

Further, according to such structure, referring to FIG. 6C, in the minimum eccentric state in the first seal interval, in a first confinement interval in which pressure in the vane chamber 18 varies from pressure on the tank to discharge pressure (an interval in operation since the vane 14 at the back of the vane chamber 18 passes the termination of the suction port 22 until the vane 14 in front of the vane chamber reaches the starting end of the discharge port 21 as described in detail later), the decrement of the volume of the vane chamber 18 in a small range at the central angle of the vane chamber can be reduced. Besides, referring to FIG. 7C, in the minimum eccentric state in the second seal interval, in a second confinement interval in which pressure in the vane chamber 18 varies from discharge pressure to pressure on the tank (an interval in operation since the vane 14 at the back of the vane chamber 18 passes the termination of the discharge port 21 until the vane 14 in front of the vane chamber reaches the starting end of the suction port 22 as described in detail later), the volume of the vane chamber 18 in a small range at the central angle of the vane chamber shows a minute inclination shifting from increase to decrease.

The radius vector is not independent in the maximum eccentric state and in the minimum eccentric state, however, if the decrement of the radius vector in the maximum eccentric state is not excessive, the radius vector can be made substantially fixed or to gradually lengthen in the minimum eccentric state in the area from the intermediate point of the first seal interval to the end point of the first seal interval and in the area from the starting point of the second seal interval to the intermediate point of the second seal interval.

Next, the connection of a passage between chambers will be described. The suction port 22 is connected to the tank not shown. The discharge port 21 communicates with a pressure chamber 26 on the side of the front body 10 via a passage not shown provided to the pressure plate 27. The pressure chamber 26 is connected via a pipe 32 on the discharge side that connects with a power cylinder not shown and others and a metering orifice 23 and is further connected to the spring chamber 36 via an upstream part 32 a of the pipe on the discharge side. Besides, the pressure chamber 26 is connected to the control valve high pressure chamber 37 via a damper orifice 20. Further, the pressure chamber 26 is also connected to the vane bottom 31 via a passage not shown.

The operation of the variable displacement vane pump 1 will be described below. When rotational driving force is input from the shaft 13, the vane 14 is rotated together with the rotor 11, being pressed on the cam ring 15 by centrifugal force and pressure at the vane bottom 31 and the volume of the vane chamber 18 increases and decreases. In the interval in which the volume increases, pressure in the vane chamber 18 drops and working fluid is sucked from the suction port 22. This interval may be called a suction interval. Pressure on the sucked working fluid is raised according to the decrease of the volume of the vane chamber 18 in the first confinement interval shown in FIG. 6C in which both the tank and the pressure chamber 26 are not connected.

The working fluid the pressure on which is raised is conducted from the discharge port 21 to the pressure chamber 26 according to the decrease of the volume of the vane chamber 18. This interval may be called a discharge interval. Further, pressure in the vane chamber 18 drops through the second confinement interval shown in FIG. 7C in which both the tank and the pressure chamber 26 are not connected and processing proceeds to a suction process again.

When the rotational speed of the pump is low, the cam ring 15 is pressed in a direction in which the volume of the pump is maximum by the compression coil spring 17 and at this time, eccentricity between the center of the inside diameter of the cam ring 15 and the rotational center Or of the rotor 11 is maximum. As discharge per one rotation of the pump is fixed in this maximum eccentric state even if the speed of the rotation varies, such an area low in the rotational speed of the pump at which the discharge per one rotation is fixed is called a fixed displacement area.

When the rotational speed of the pump increases and the discharge increases, pressure loss in the metering orifice 23 increases, rightward force due to pressure difference between both ends of the control valve 30 overcomes the leftward force of the spring 30 c, and the control valve 30 in FIG. 2 is moved rightward. At this time, working fluid on the downstream side of the damper orifice 20 is conducted via the opened control valve 30 into the first fluid pressure chamber 34, the cam ring 15 is swung in a direction in which the eccentricity of the cam ring 15 is reduced, and discharge per one rotation is reduced. Such an area high in the rotational speed of the pump in which discharge per one rotation decreases as the rotational speed of the pump increases is called a variable displacement area.

It is known that in the variable displacement vane pump 1, primary causes that cause noise are different in the fixed displacement area and in the variable displacement area, it is considered that in the fixed displacement area, pressure pulsation by the separation of the vane in which an end of the vane 14 is separated from the inner peripheral face of the cam ring 15 is the primary cause that causes noise, and it is considered that in the variable displacement area, vibration by a peak of pressure caused in the vane chamber 18 is the primary cause that causes noise.

FIG. 8 is a schematic drawing showing a section of a local part for explaining the mechanism of the separation of the vane caused in the structure before improvement of the variable displacement vane pump 1.

As high oil pressure acts on only the front of the vane 14 when the vane chamber 18 proceeds from the suction process to a discharge process, supposing operation in the first seal interval in the maximum eccentric state, frictional force opposite to a projected direction increases when the vane 14 is pressed in the slot 29 of the rotor 11, the frictional force becomes larger than centrifugal force that acts on the vane 14 and oil pressure at the vane bottom 31, and force in the direction in which the vane is projected out of the slot 29 may be reduced. Further, when pressure in the vane chamber 18 varies by proceeding from the suction process to the discharge process or proceeding from the discharge process to the suction process, the pressure balance of each vane chamber 18 varies and the shaft 13 is deformed. The separation of the vane is apt to occur. The separation of the vane is that the rotor 11 is moved by the quantity of the deformation of the shaft 13 and the quantity of clearance between the shaft 13 and the rotor 11 and the vane 14 is also moved in a direction in which the vane is separated from the inner peripheral face of the cam ring 15 by friction in the slot 29 of the rotor 11.

As oil rapidly flows from the high pressure side to the low pressure side when the separation of the vane occurs, pressure pulsation is caused. Especially, as a first half of the first seal interval is an area in which the vane chamber 18 in front of the vane 14 has a peak of pressure, a phenomenon of the pressure pulsation is apt to occur.

Then, in the improved structure of the variable displacement vane pump 1 equivalent to the first embodiment, as the inner peripheral face of the cam ring 15 has such a shape that the radius vector shortens in the first seal interval as described above, the separation of the vane is restrained and pressure pulsation can be restrained.

Similarly, when the vane chamber 18 proceeds from the discharge process to the suction process, high oil pressure acts on only the back of the vane 14, frictional force is produced in the slot 29 of the rotor 11, and the separation of the vane is easily caused. Especially, as the vane chamber 18 in front is an area having a peak of pressure in the area from the intermediate point to the end point of the second seal interval, the separation of the vane is apt to occur.

Then, in the improved structure of the variable displacement vane pump 1 equivalent to the first embodiment, as the inner peripheral face of the cam ring 15 has such a shape that the radius vector gradually shortens in the second seal interval as described above, the separation of the vane can be restrained.

FIG. 9 is a characteristic line drawing showing pressure to an angle for explaining a peak of pressure in the vane chamber 18 caused in the structure before improvement of the variable displacement vane pump 1.

When the vane chamber 18 is in the first confinement interval, supposing operation in the first seal interval in the minimum eccentric state, both the suction port 22 and the discharge port 21 are not connected, when the volume of the vane chamber 18 decreases at this time, pressure in a pump room rises over discharge pressure and a peak of pressure shown in FIG. 9 is caused.

The decrement of the volume in the first confinement interval since the vane 14 at the back of the vane chamber 18 passes the termination of the suction port 22 until the vane 14 in front reaches the starting end of the discharge port 21 has an effect upon the peak of pressure. Difference for this while between the volume when the vane 14 in front passes and the volume when the vane 14 at the back passes is equivalent to the compressed quantity of the volume. However, as the first confinement interval is a very short interval, the volume of the vane chamber 18 in the first confinement interval decreases when the radius vector is shorter at the end point of the starting point and the end point of the first seal interval and it can be said that the peak of pressure is apt to be caused.

Then, in the improved structure of the variable displacement vane pump 1 equivalent to the first embodiment, as the inner peripheral face of the cam ring 15 has such a shape that the radius vector is substantially fixed or gradually lengthens in the area from the intermediate point to the end point of the first seal interval in the minimum eccentric state as described above, radiuses at the starting point and at the end point of the first seal interval are made to approximate the same value, the decrement of the volume is restrained, and the peak of pressure can be reduced.

Similarly, when the vane chamber 18 is in the second confinement interval, the peak of pressure is also apt to be caused as the volume of the vane chamber 18 decreases.

The decrement of the volume in the second confinement interval since the vane 14 at the back of the vane chamber 18 passes the termination of the discharge port 21 until the vane 14 in front reaches the starting end of the suction port 22 has an effect upon the peak of pressure. However, as the second confinement interval is also a very short interval, the volume of the vane chamber 18 in the second confinement interval decreases when the radius vector is shorter at the end point of the starting point and the end point of the second seal interval and it can be said that the peak of pressure is apt to be caused.

Then, in the improved structure of the variable displacement vane pump 1 equivalent to the first embodiment, as the inner peripheral face of the cam ring 15 has such a shape that the radius vector is substantially fixed or gradually lengthens in the area from the starting point to the intermediate point of the second seal interval in the minimum eccentric state as described above, the radiuses at the starting point and at the end point of the second seal interval are made to approximate the same value, the decrement of the volume is restrained, and the peak of pressure can be reduced.

As the variable displacement vane pump 1 equivalent to the first embodiment has effect that in the maximum eccentric state in which a shape of the inner peripheral face of the cam ring 15 is equivalent to its shape in the fixed displacement area, the separation of the vane is restrained and in the minimum eccentric state which is a part of the variable displacement area, the peak of pressure is reduced, noise can be reduced both in the fixed displacement area and in the variable displacement area.

Besides, in the variable displacement vane pump 1 equivalent to the first embodiment, pressure in the vane chamber 18 varies from pressure on the tank to discharge pressure in the first confinement interval and varies from discharge pressure to pressure on the tank in the second confinement interval. As the pressure fluctuation occurs in the first confinement interval and in the second confinement interval, which are opposite, oil pressure is produced by difference in pressure. Further, when the oil pressure acts on the inner peripheral face of the cam ring 15, the cam ring 15 is vibrated, as a result, the variation of a flow rate and pressure pulsation are caused, and noise may be made. Then, as the unbalance of pressure that causes the variation of a flow rate and pressure pulsation can be softened when the plurality of odd pieces of slots 29 and the plurality of odd pieces of vanes 14 are provided to the rotor 11, the noise can be more reduced.

Further, the inner peripheral face of the cam ring 15 for example may be also formed in only the area from the starting point of the first seal interval (the termination of the suction port 22) to its intermediate point (the intermediate point of the termination of the suction port 22 and the starting end of the discharge port 21) in the maximum eccentric state so that the radius vector gradually shortens according to the rotation of the rotor 11, and the inner peripheral face of the cam ring may be also formed in only at least a part of the area from the intermediate point of the first seal interval (the intermediate point of the termination of the suction port 22 and the starting end of the discharge port 21) to its end point (the starting end of the discharge port 21) in the minimum eccentric state so that the radius vector is substantially fixed or gradually lengthens according to the rotation of the rotor 11. Such configuration is effective to prevent noise from being made because of pressure pulsation and vibration especially on the side of the first seal interval.

In addition, the inner peripheral face of the cam ring 15 for example may be also formed in only the area from the intermediate point of the second seal interval (the intermediate point of the termination of the discharge port 21 and the starting end of the suction port 22) to its end point (the starting end of the suction port 22) in the maximum eccentric state so that the radius vector gradually shortens according to the rotation of the rotor 11, and the inner peripheral face of the cam ring may be also formed in only at least a part of the area from the starting point of the second seal interval (the termination of the discharge port 21) to its intermediate point (the intermediate point of the termination of the discharge port 21 and the starting end of the suction port 22) in the minimum eccentric state so that the radius vector is substantially fixed or gradually lengthens according to the rotation of the rotor 11. Such configuration is effective to prevent noise from being made because of pressure pulsation and vibration especially on the side of the second seal interval.

Second Embodiment

A variable displacement vane pump equivalent to a second embodiment is similar to the other configuration in the first embodiment except that in comparison with the variable displacement vane pump 1 equivalent to the first embodiment, a shaft 13 is rotatively driven by an engine of a vehicle and an inner peripheral face of a cam ring 15 is formed in at least one of at least a part of an area from an intermediate point of a first seal interval (an intermediate point of a termination of a suction port 22 and a starting end of a discharge port 21) to its end point (the starting end of the discharge port 21) while the vehicle is run and at least a part of an area from a starting point of a second seal interval (a termination of the discharge port 21) to its intermediate point (an intermediate point of the termination of the discharge port 21 and a starting end of the suction port 22) so that a radius vector is substantially fixed or gradually lengthens according to the rotation of the rotor 11.

In the variable displacement vane pump equivalent to the second embodiment, in addition to the action and the effect by the variable displacement vane pump 1 equivalent to the first embodiment, a peak of pressure in a vane chamber 18 is reduced while the vehicle is run and noise can be prevented from being made.

Third Embodiment

A variable displacement vane pump equivalent to a third embodiment is similar to the other configuration of the first embodiment except that in comparison with the variable displacement vane pump 1 equivalent to the first embodiment, a shaft 13 is rotatively driven by an engine of a vehicle and an inner peripheral face of a cam ring 15 is formed in at least one of at least a part of an area from an intermediate point of a first seal interval (an intermediate point of a termination of a suction port 22 and a starting end of a discharge port 21) to its end point (the starting end of the discharge port 21) when engine speed is 1500 rpm or more every minute and at least a part of an area from a starting point of a second seal interval (a termination of the discharge port 21) to its intermediate point (an intermediate point of the termination of the discharge port 21 and a starting end of the suction port 22) so that a radius vector is substantially fixed or gradually lengthens according to the rotation of a rotor 11.

In the variable displacement vane pump equivalent to the third embodiment, in addition to the action and the effect by the variable displacement vane pump 1 equivalent to the first embodiment, when engine speed the noise of which is apt to come into question especially in a variable displacement area is 1500 rpm or more every minute, a peak of pressure in a vane chamber 18 is restrained and noise can be prevented from being made.

Fourth Embodiment

A variable displacement vane pump equivalent to a fourth embodiment is similar to the other configuration of the first embodiment except that in comparison with the variable displacement vane pump 1 equivalent to the first embodiment, an inner peripheral face of a cam ring 15 is formed so that in a maximum eccentric state, at least one of an area from a starting point of a first seal interval (a termination of a suction port 22) to its intermediate point (an intermediate point of the termination of the suction port 22 and a starting end of a discharge port 21) and an area from an intermediate point of a second seal interval (an intermediate point of a termination of the discharge port 21 and a starting end of the suction port 22) to its end point (the starting end of the suction port 22) and areas before and after at least the one that connect with at least the one are connected by a higher order curve and the inner peripheral face of the cam ring is formed so that in a minimum eccentric state, at least one of at least a part of an area from the intermediate point of the first seal interval (the intermediate point of the termination of the suction port 22 and the starting end of the discharge port 21) to its end point (the starting end of the discharge port 21) and at least a part of an area from a starting point of the second seal interval (the termination of the discharge port 21) to its intermediate point (the intermediate point of the termination of the discharge port 21 and the starting end of the suction port 22) and areas before and after at least the one are connected by a higher order curve.

In the variable displacement vane pump equivalent to the fourth embodiment, in addition to the action and the effect by the variable displacement vane pump 1 equivalent to the first embodiment, as the inner peripheral face of the cam ring 15 can have a smoothly connected shape, the separation of the vane 14 is more restrained and noise can be remarkably prevented from being made.

Fifth Embodiment

FIGS. 10A and 10B are schematic drawings showing relative positional relation of a rotor 11, a cam ring 15, a discharge port 21 and a suction port 22 with a supporting face 38 provided to an adapter 12 in a variable displacement vane pump equivalent to a fifth embodiment of the present invention, FIG. 10A is the schematic drawing showing a maximum eccentric state, and FIG. 10B is the schematic drawing showing a minimum eccentric state. As components not shown of the variable displacement vane pump equivalent to the fifth embodiment are the same as the components in the configuration of the variable displacement vane pump 1 equivalent to the first embodiment, the same reference sign is allocated, the description is omitted, and only different components will be described below.

In the variable displacement vane pump equivalent to the fifth embodiment, eccentricity between the cam ring 15 and the rotor 11 is controlled by swinging or rolling the cam ring 15 in a state in which the cam ring 15 is supported by the supporting face 38 provided on the side of a discharge port 21 of an inner peripheral face of the adapter 12. The center Oc of an inside diameter of the cam ring 15 is provided so that it is located on the side of the suction port 22 apart from the rotational center Or of the rotor 11 in an unloaded condition in which differential pressure between pressure on the side of the suction port 22 and pressure on the side of the discharge port 21 does not act on a shaft 13, the rotor 11 and the cam ring 15 and a relative position to a port reference line Lp is located on the side of the discharge port 21 apart from a relative position in the unloaded condition in a state in which the shaft 13 is elastically deformed on the side of the suction port 22 by the action of the differential pressure. Further, the cam ring 15 is rollably supported by the supporting face 38 provided on the side of the discharge port 21 of the inner peripheral face of the adapter 12, and the cam ring is formed so that the center Oc of the inside diameter of the cam ring 15 gradually separates on the side of the discharge port 21 from the port reference line Lp as the supporting face 38 is rolled in a direction from a maximum eccentric state of the cam ring 15 to a minimum eccentric state. The configuration of the other components is similar to the configuration of the other components of the variable displacement vane pump 1 equivalent to the first embodiment.

In the variable displacement vane pump equivalent to the fifth embodiment, in addition to the action and the effect by the variable displacement vane pump 1 equivalent to the first embodiment, as eccentricity between the cam ring 15 and the rotor 11 can be controlled by a shape of the supporting face 38, radius vectors in a fixed displacement area and in a variable displacement area can be more effectively controlled and the effect of the prevention of noise can be increased.

The center Oc of the inside diameter of the cam ring 15 is provided so that the relative position is located on the side of the suction port 22 apart from the port reference line Lp in the unloaded condition in which no differential pressure acts and is located on the side of the discharge port 21 apart from the relative position in the unloaded condition in a state in which differential pressure acts, the cam ring 15 is rollably supported by the supporting face 38 provided on the side of the discharge port 21 of the inner peripheral face of the adapter 12, and when the cam ring is formed so that the center Oc of the inside diameter of the cam ring 15 gradually separates on the side of the discharge port 21 from the port reference line Lp as the supporting face 38 is rolled in the direction from the maximum eccentric state of the cam ring 15 to the minimum eccentric state, a relative position to a first seal interval can be controlled according to an operating condition.

Concretely, as shown in FIG. 10A showing the maximum eccentric state, as a port reference angle (a port timing angle) θ which is a relative angle between a line that joins the rotational center Or of the rotor 11 and the center Oc of the inside diameter of the cam ring 15 and the port reference line Lp is large at low rotation speed, radius vectors in the first seal interval have a tendency to gradually shorten and hereby, the separation of a vane can be more restrained.

Besides, as shown in FIG. 10B showing the minimum eccentric state, as the port reference angle (the port timing angle) θ is small at high rotation speed, the variation of the volume in the first seal interval can be reduced and the occurrence of a peak of pressure can be restrained.

Further, even if the cam ring 15 is relatively moved by differential pressure between pressure on the side of the suction port 22 and pressure on the side of the discharge port 21, the port reference angle (the port timing angle) θ can be optimized.

Accordingly, the above-mentioned configuration is effective as a function for preventing noise from being made by pressure pulsation and vibration on the side of the first seal interval.

Sixth Embodiment

A variable displacement vane pump equivalent to a sixth embodiment is similar to the other configuration of the first embodiment except that in comparison with the variable displacement vane pump 1 equivalent to the first embodiment, an inner peripheral face of a cam ring 15 is formed so that in a maximum eccentric state, a radius vector gradually shortens according to the rotation of a rotor 11 in at least one of an area of a first seal interval (an area from a termination of a suction port 22 to a starting end of a discharge port 21) in a rotational direction of the rotor 11 and an area of a second seal interval (an area from a termination of the discharge port 21 to a starting end of the suction port 22) and the inner peripheral face of the cam ring is formed so that in a minimum eccentric state, the radius vector is substantially fixed or gradually lengthens according to the rotation of the rotor 11 in at least one of at least a part of the area of the first seal interval (the area from the termination of the suction port 22 to the starting end of the discharge port 21) and at least a part of the area of the second seal interval (the area from the termination of the discharge port 21 to the starting end of the suction port 22).

In the variable displacement vane pump equivalent to the sixth embodiment, in addition to the action and the effect by the variable displacement vane pump 1 equivalent to the first embodiment, as the inner peripheral face of the cam ring 15 has such a shape that the separation can be prevented in the whole area in which the separation of a vane 14 may be caused, the occurrence of noise can be remarkably restrained (prevented). Incidentally, the configuration in the second embodiment, the third embodiment and the fifth embodiment can be also applied to the variable displacement vane pump equivalent to the sixth embodiment and in that case, the effect described in each embodiment is similarly produced in addition to the above-mentioned effects.

Seventh Embodiment

A variable displacement vane pump equivalent to a seventh embodiment is similar to the other configuration of the first embodiment except that in comparison with the variable displacement vane pump 1 equivalent to the first embodiment, an inner peripheral face of a cam ring 15 is formed so that in a maximum eccentric state in which the cam ring 15 is relatively moved from the side of a suction port 22 to the side of a discharge port 21 because differential pressure between pressure on the side of the suction port 22 and pressure on the side of the discharge port 21 acts on a shaft 13, a rotor 11 and the cam ring 15, compared with an unloaded condition in which no differential pressure acts, a radius vector gradually shortens according to the rotation of the rotor 11 in at least one of an area of a first seal interval (an area from a termination of the suction port 22 to a starting end of the discharge port 21) and an area of a second seal interval (an area from a termination of the discharge port 21 to a starting end of the suction port 22) and the inner peripheral face of the cam ring is formed so that in the minimum eccentric state, the radius vector is substantially fixed or gradually lengthens according to the rotation of the rotor 11 in at least one of the area of the first seal interval (the area from the termination of the suction port 22 to the starting end of the discharge port 21) and the area of the second seal interval (the area from the termination of the discharge port 21 to the starting end of the suction port 22).

In the variable displacement vane pump equivalent to the seventh embodiment, even if the cam ring 15 is relatively moved by differential pressure between pressure on the side of the suction port 22 and pressure on the side of the discharge port 21, pressure pulsation in the maximum eccentric state and vibration in the minimum eccentric state can be restrained and the occurrence of noise can be effectively prevented. Incidentally, the configuration described in the second embodiment, the third embodiment and the fifth embodiment can be also applied to the variable displacement vane pump equivalent to the seventh embodiment and in that case, the effect described in each embodiment is similarly produced in addition to the above-mentioned effect.

Preferred embodiments of the present invention have been described above, but various changes thereto may be made without departing from the scope and spirit of the present invention. 

1. A variable displacement vane pump for transmitting steering operation on a steering wheel to a steered wheel and supplying working fluid to a steering gear for a vehicle that generates steering assist force by hydraulic pressure of the working fluid, the variable displacement vane pump comprising: a pump housing provided with a pump element storage part; a driving shaft journaled to the pump housing; a rotor provided in the pump housing, rotatively driven by the driving shaft and provided with a plurality of slots in a circumferential direction; a plurality of vanes provided in a freely projecting/retreating manner in the plurality of slots; a cam ring annularly formed movably on/over the pump element storage part and forming a plurality of pump rooms together with the rotor and the plurality of vanes on an inner peripheral side; and a cam ring control mechanism that is provided to the pump housing and controls eccentricity to the rotor of the cam ring, wherein: the pump housing is provided with a suction port open to an area in which volume of the plurality of pump rooms increases according to rotation of the rotor and a discharge port open to an area in which the volume of the plurality of pump rooms decreases; and an inner peripheral face of the cam ring is formed to be a state that in a maximum eccentric state that in which eccentricity to the rotor of the cam ring is maximum, a distance to the rotational center of the rotor gradually shortens according to the rotation of the rotor in at least one of an area from a termination of the suction port to an intermediate point of the termination of the suction port and a starting end of the discharge port and an area from an intermediate point of a termination of the discharge port and a starting end of the suction port to the starting end of the suction port in a rotational direction of the rotor, and the inner peripheral face of the cam ring is formed to be a state that in a minimum eccentric state in which the eccentricity to the rotor of the cam ring is minimum, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of an area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and at least a part of an area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port.
 2. The variable displacement vane pump according to claim 1, wherein: the driving shaft is rotatively driven by an engine of the vehicle; and the inner peripheral face of the cam ring is formed to be a state that when the vehicle is run, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port.
 3. The variable displacement vane pump according to claim 1, wherein: the driving shaft is rotatively driven by the engine of the vehicle; and the inner peripheral face of the cam ring is formed to be a state that when engine speed is 1500 rpm or more every minute, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the intermediate port of the termination of the discharge port and the starting end of the suction port.
 4. The variable displacement vane pump according to claim 1, wherein: the inner peripheral face of the cam ring is formed to be a state that in the maximum eccentric state, at least one of the area from the termination of the suction port to the intermediate point of the termination of the suction port and the starting end of the discharge port and the area from the intermediate point of the termination of the discharge port and the starting end of the suction port to the starting end of the suction port and areas before and after at least the one that connect with at least the one are connected by a higher order curve; and the inner peripheral face of the cam ring is formed to be a state that in the minimum eccentric state, at least one of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and the area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port and areas before and after at least the one that connect with at least the one are connected by the higher order curve.
 5. The variable displacement vane pump according to claim 1, wherein: the inner peripheral face of the cam ring is formed to be a state that in the minimum eccentric state, the distance to the rotational center of the rotor gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port.
 6. The variable displacement vane pump according to claim 1, wherein: the eccentricity to the rotor of the cam ring is controlled by swinging or rolling the cam ring in a state in which the cam ring is supported by a supporting face provided on a side of the discharge port of an inner peripheral face of the pump element storage part.
 7. The variable displacement vane pump according to claim 6, wherein: the center of an inside diameter of the cam ring is located on the side of the suction port apart from the center of the rotor in an unloaded condition in which differential pressure between pressure on the side of the suction port and pressure on the side of the discharge port does not act on the driving shaft, the rotor and the cam ring, and in a state in which the driving shaft is elastically deformed on the side of the suction port by the action of the differential pressure, a relative position of the center of the inside diameter of the cam ring to a port reference line is located on the side of the discharge port apart from a relative position in the unloaded condition; the cam ring is rollably supported by a supporting face provided on the side of the discharge port of the inner peripheral face of the pump element storage part; and the supporting face is formed to be a state that as the cam ring is rolled in a direction from the maximum eccentric state to the minimum eccentric state, the center of the inside diameter of the cam ring gradually separates on the side of the discharge port from the port reference line.
 8. The variable displacement vane pump according to claim 1, wherein: the inner peripheral face of the cam ring is formed to be a state that in the maximum eccentric state, the distance to the rotational center of the rotor gradually shortens according to the rotation of the rotor in the area from the termination of the suction port to the intermediate point of the termination of the suction port and the starting end of the discharge port in a rotational direction of the rotor; and the inner peripheral face of the cam ring is formed to be a state that in the minimum eccentric state, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least a part of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port.
 9. The variable displacement vane pump according to claim 8, wherein: the inner peripheral face of the cam ring is formed to be a state that in the maximum eccentric state, the distance to the rotational center of the rotor gradually shortens according to the rotation of the rotor in the area from the termination of the suction port to the intermediate point of the termination of the suction port and the starting end of the discharge port and in the area from the intermediate point of the termination of the discharge port and the starting end of the suction port to the starting end of the suction port in the rotational direction of the rotor; and the inner peripheral face of the cam ring is formed to be a state that in the minimum eccentric state, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least a part of the area from the intermediate point of the termination of the suction port and the starting end of the discharge port to the starting end of the discharge port and in at least a part of the area from the termination of the discharge port to the intermediate point of the termination of the discharge port and the starting end of the suction port.
 10. The variable displacement vane pump according to claim 1, wherein: the plurality of odd pieces of slots and the plurality of odd pieces of vanes are provided to the rotor.
 11. A variable displacement vane pump for transmitting steering operation on a steering wheel to a steered wheel and supplying working fluid to a steering gear for a vehicle that generates steering assist force by hydraulic pressure of the working fluid, the variable displacement vane pump comprising: a pump housing provided with a pump element storage part; a driving shaft journaled to the pump housing; a rotor provided in the pump housing, rotatively driven by the driving shaft and provided with a plurality of slots in a circumferential direction; a plurality of vanes provided in a freely projecting/retreating manner in the plurality of slots; a cam ring annularly formed movably on/over the pump element storage part and forming a plurality of pump rooms together with the rotor and the plurality of vanes on an inner peripheral side; and a cam ring control mechanism that is provided to the pump housing and controls eccentricity to the rotor of the cam ring, wherein: the pump housing is provided with a suction port open to an area in which volume of the plurality of pump rooms increases according to rotation of the rotor and a discharge port open to an area in which the volume of the plurality of pump rooms decreases; and an inner peripheral face of the cam ring is formed to be a state that in a maximum eccentric state in which eccentricity to the rotor of the cam ring is maximum, a distance to the rotational center of the rotor gradually shortens according to the rotation of the rotor in at least one of an area from a termination of the suction port to a starting end of the discharge port in a rotational direction of the rotor and an area from a termination of the discharge port to a starting end of the suction port, and the inner peripheral face of the cam ring is formed to be a state that in a minimum eccentric state in which the eccentricity to the rotor of the cam ring is minimum, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.
 12. The variable displacement vane pump according to claim 11, wherein: the driving shaft is rotatively driven by an engine of the vehicle; and the inner peripheral face of the cam ring is formed to be a state that when the vehicle is run, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.
 13. The variable displacement vent pump according to claim 11, wherein: the driving shaft is rotatively driven by the engine of the vehicle; and the inner peripheral face of the cam ring is formed to be a state that when engine speed is 1500 rpm or more every minute, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.
 14. The variable displacement vane pump according to claim 11, wherein: the eccentricity to the rotor of the cam ring is controlled by swinging or rolling the cam ring in a state in which the cam ring is supported by a supporting face provided on a side of the discharge port of an inner peripheral face of the pump element storage part.
 15. The variable displacement vane pump according to claim 14, wherein: the center of an inside diameter of the cam ring is located on the side of the suction port based upon a port reference line that joins an intermediate point of the termination of the suction port and the starting end of the discharge port and the center of the rotor in an unloaded condition in which differential pressure between pressure on the side of the suction port and pressure on the side of the discharge port does not act on the driving shaft, the rotor and the cam ring, and a relative position of the center of the inside diameter of the cam ring based upon the port reference line in a state in which the driving shaft is elastically deformed on the side of the suction port by the action of the differential pressure is located on the side of the discharge port apart from a relative position in the unloaded condition; the cam ring is rollably supported by a supporting face provided on the side of the discharge port of the inner peripheral face of the pump element storage part; and the supporting face is formed to be a state that as the cam ring is rolled in a direction from the maximum eccentric state to the minimum eccentric state, the center of the inside diameter of the cam ring gradually separates from the port reference line.
 16. A variable displacement vane pump for transmitting steering operation on a steering wheel to a steered wheel and supplying working fluid to a steering gear for a vehicle that generates steering assist force by the hydraulic pressure of the working fluid, the variable displacement vane pump comprising: a pump housing provided with a pump element storage part; a driving shaft journaled to the pump housing; a rotor provided in the pump housing, rotatively driven by the driving shaft and provided with a plurality of slots in a circumferential direction; a plurality of vanes provided in a freely projecting/retreating manner in the plurality of slots; a cam ring annularly formed movably on/over the pump element storage part and forming a plurality of pump rooms together with the rotor and the plurality of vanes on an inner peripheral side; and a cam ring control mechanism that is provided to the pump housing and controls eccentricity to the rotor of the cam ring, wherein: the pump housing is provided with a suction port open to an area in which volume of the plurality of pump rooms increases according to rotation of the rotor and a discharge port open to an area in which the volume of the plurality of pump rooms decreases; and an inner peripheral face of the cam ring is formed to be a state that in a state in which the cam ring is relatively moved from the side of the suction port to the side of the discharge port by the action on the driving shaft, the rotor and the cam ring of differential pressure between pressure on the side of the suction port and pressure on the side of the discharge port, compared with an unloaded condition in which no differential pressure acts and in a maximum eccentric state in which the eccentricity to the rotor of the cam ring is maximum, a distance to the rotational center of the rotor gradually shortens according to the rotation of the rotor in at least one of an area from a termination of the suction port to a starting end of the discharge port and an area from a termination of the discharge port to a starting end of the suction port in a rotational direction of the rotor, and the inner peripheral face of the cam ring is formed to be a state that in a minimum eccentric state in which the eccentricity to the rotor of the cam ring is minimum, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.
 17. The variable displacement vane pump according to claim 16, wherein: the driving shaft is rotatively driven by an engine of the vehicle; and the inner peripheral face of the cam ring is formed to be a state that when the vehicle is run, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.
 18. The variable displacement vane pump according to claim 16, wherein: the driving shaft is rotatively driven by the engine of the vehicle; and the inner peripheral face of the cam ring is formed to be a state that when engine speed is 1500 rpm or more every minute, the distance to the rotational center of the rotor is substantially fixed or gradually lengthens according to the rotation of the rotor in at least one of at least a part of the area from the termination of the suction port to the starting end of the discharge port and at least a part of the area from the termination of the discharge port to the starting end of the suction port.
 19. The variable displacement vane pump according to claim 16, wherein: the eccentricity to the rotor of the cam ring is controlled by swinging or rolling the cam ring in a state in which the cam ring is supported by a supporting face provided on a side of the discharge port of an inner peripheral face of the pump element storage part.
 20. The variable displacement vane pump according to claim 19, wherein: the center of an inside diameter of the cam ring is located on the side of the suction port based upon a port reference line that joins an intermediate point of the termination of the suction port and the starting end of the discharge port and the center of the rotor in an unloaded condition in which differential pressure between pressure on the side of the suction port and pressure on the side of the discharge port does not act on the driving shaft, the rotor and the cam ring, and a relative position based upon the port reference line in a state in which the driving shaft is elastically deformed on the side of the suction port by the action of the differential pressure is located on the side of the discharge port apart from a relative position in the unloaded condition; the cam ring is rollably supported by the supporting face provided on the side of the discharge port of the inner peripheral face of the pump element storage part; and the supporting face is formed to be a state that the center of the inside diameter of the cam ring gradually separates from the port reference line as the cam ring is rolled in a direction from the maximum eccentric state to the minimum eccentric state. 